My Outlook 2007 (OS XP2) suddenly won't send emails that have attachments, whatever the size.
It says "Preparing to Send & Receive", but nothing happens and it eventually times out.
I have recently installed Bit Defender, downloaded Microsoft Updates, and repaired Office 2007.
I ran Scanpst.exe which found some errors and repaired them. I have carried out anti virus and malaware scans. I have tried to send with Bit Defender switched off. I have also tried to send to myself.
I have no problem with incoming or outgoing simple emails.

Help would be appreciated.